Weather & Climate in Chatham, IL
Temperature, precipitation, air quality, natural hazards, and monthly weather data.
Chatham experiences four distinct seasons with an average annual temperature of 54°F (12°C). Winters average 28°F in January while summers reach 77°F in July. Annual precipitation totals 38.0 inches. The area receives 21.8 inches of snow annually, a moderate snowfall amount. Air quality is rated Good with a median AQI of 41. 72% of days have good air quality. The city sits at an elevation of 598 feet.
Temperature
28°F Jan (-2°C)
77°F Jul (25°C)
| Annual Average | 54.0°F |
| 0% below US avg | |
| January Average | 28°F (-2°C) |
| July Average | 77°F (25°C) |
Geography
| Elevation | 598 ft (182 m) |
| Area | 2.7 sq mi (7.0 km²) |
| Population Density | 1,989/sq mi |
| Coordinates | 39.6745°N, 89.6933°W |
| Timezone | America/Chicago |
| County | Sangamon County County |
| Nearest Airport | St Louis Regional (ALN) 57 miles away |
Precipitation & Snow
Air Quality
| AQI Median | 41.0 |
| Rating | Good |
| Good Days % | 71.9% |
| Unhealthy Days | 1 |
Natural Hazard Risk
| Overall Risk | Relatively Moderate |
| Risk Score | 91.7 / 100 |
| Social Vulnerability | 32.0 / 100 |
| Community Resilience | 92.2 / 100 |
Hazard Breakdown
| Tornado | Relatively High |
| Hurricane | Very Low |
| Earthquake | Relatively Moderate |
| Wildfire | Very Low |
| Flood | Relatively Moderate |
| Hail | Relatively High |
| Strong Wind | Relatively High |
| Heat Wave | Relatively Moderate |
| Winter Weather | Relatively High |
| Lightning | Relatively High |
| Ice Storm | Relatively Moderate |
| Drought | Relatively High |
| Cold Wave | Relatively High |
| Landslide | Relatively Low |
Source: FEMA National Risk Index v1.20 (Dec 2025)
Earthquake History
10 earthquakes (M2.5+) recorded within 150 km since 1990. Strongest on record: M3.4.
| Mar 2, 1990 | 9 km NW of Vernon, Illinois | M3.4 | 102 km | 0 km |
| May 13, 2025 | 7 km SSW of Lerna, Illinois | M3.3 | 122 km | 10 km |
| Jan 29, 1993 | 7 km WNW of Brownstown, Illinois | M3.2 | 91 km | 5 km |
| Jul 1, 2017 | 9 km SSE of Mulberry Grove, Illinois | M3.1 | 100 km | 17 km |
| Sep 5, 2004 | 3 km WNW of Saint Peter, Illinois | M2.9 | 112 km | 33 km |
| Apr 29, 2022 | 1 km SSW of Peerless Park, Missouri | M2.8 | 145 km | 8 km |
| Mar 28, 2024 | 1 km NNE of Germantown, Illinois | M2.8 | 124 km | 24 km |
| May 5, 2008 | 3 km SSE of Fenton, Missouri | M2.8 | 146 km | 19 km |
| Sep 19, 2024 | 1 km S of Old Monroe, Missouri | M2.6 | 124 km | 2 km |
| Jan 15, 1998 | 1 km SSE of Fenton, Missouri | M2.5 | 145 km | 16 km |
Source: USGS Earthquake Catalog (M2.5+, 1990-2025). Sorted by magnitude.
Tornado History
681 tornadoes (EF0+) recorded within 100 km since 1950. Strongest on record: EF4. Total: 23 fatalities, 698 injuries.
| Date | Rating | Distance | Path | Fatalities |
| May 13, 1995 | EF4 | 93 km | 7.0 mi | 0 |
| May 5, 1977 | EF4 | 74 km | 7.3 mi | 0 |
| Mar 20, 1976 | EF4 | 78 km | 63.7 mi | 0 |
| Jun 14, 1957 | EF4 | 8 km | 4.3 mi | 2 |
| Apr 4, 2023 | EF3 | 91 km | 19.9 mi | 0 |
| Dec 1, 2018 | EF3 | 39 km | 12.5 mi | 0 |
| Apr 19, 2011 | EF3 | 28 km | 4.3 mi | 0 |
| Dec 31, 2010 | EF3 | 37 km | 3.6 mi | 0 |
| Aug 19, 2009 | EF3 | 33 km | 24.3 mi | 0 |
| May 10, 2003 | EF3 | 89 km | 17.5 mi | 0 |
| Jun 1, 1999 | EF3 | 40 km | 10.0 mi | 1 |
| Apr 19, 1996 | EF3 | 78 km | 9.4 mi | 0 |
| Apr 19, 1996 | EF3 | 47 km | 14.5 mi | 0 |
| May 13, 1995 | EF3 | 85 km | 25.0 mi | 0 |
| May 9, 1995 | EF3 | 23 km | 50.0 mi | 0 |
| May 1, 1983 | EF3 | 65 km | 4.0 mi | 0 |
| Jul 26, 1978 | EF3 | 16 km | 8.9 mi | 0 |
| Aug 21, 1977 | EF3 | 94 km | 26.9 mi | 6 |
| Aug 6, 1977 | EF3 | 6 km | 4.1 mi | 0 |
| Jul 28, 1976 | EF3 | 94 km | 0.1 mi | 0 |
Source: NOAA Storm Prediction Center (EF0+, 1950-2024, US only).
Monthly Weather
| Month | Avg Temperature | Precipitation | Summary |
|---|---|---|---|
| January | 28°F (-2°C) | 2.0 in | Coldest |
| February | 32°F (0°C) | 1.9 in | Driest |
| March | 43°F (6°C) | 2.8 in | |
| April | 54°F (12°C) | 4.0 in | |
| May | 65°F (18°C) | 4.5 in | |
| June | 74°F (23°C) | 4.6 in | Wettest |
| July | 77°F (25°C) | 3.9 in | Warmest |
| August | 75°F (24°C) | 3.4 in | |
| September | 68°F (20°C) | 2.9 in | |
| October | 56°F (13°C) | 3.3 in | |
| November | 44°F (6°C) | 2.7 in | |
| December | 33°F (0°C) | 2.2 in |
Chatham has a seasonal temperature swing of 49°F / from 28°F in January to 77°F in July. Total annual precipitation is 38.0 inches, with June being the wettest month (4.6") and February the driest (1.9").